kly-site updated January 2017
Inca's Balsa Log Raft
Theory for Daggerboard navigation
Guaras is a steering system - and not a keel supplement
When the Spaniards meet the Inca Balsa rafts, they were surprised by the cargo they were able to carry - but too the fact, that those rafts were navigated without a rudder, but nevertheless were able to go as close or better to the wind than the Spanish ships.
But how that technology worked is still today something of a mystery.
Guaras work only together with the wind
One of the FIRST photos - showing two of the LAST balsas
- around 120 years ago -
A balsa raft - a Kontiki-raft is a raft of balsa-wood-logs with Guaras plunged-in (inserted) between the logs to control that leeway, as every sail-craft has.
Guara they called it and Guara is the accepted word for those daggerboards, centerboards, leeboards, lifting keels, swinging swords - words as all are synonyms for nearly the same - retractable keels. The word Guara is not a Quechua word - seems to come from a language nearer to Equator.
Our model raft has only one centered mast and a number of Guaras, as can be plunged in between the trunks where we want.
This Guara-system has worked in hundreds of years, even if Thor Heyerdahl had to rediscover it. Opposite the classic stern rudder as need streaming water to change direction of a boat - a Guara-raft can turn statically = on the site.
We have five themes:
A): Balanced side sliding
Balance of Side Sliding is a theory as seems serviceable in all cases and for every floating vessel - rafts as well as boats, monohulls and multihulls.
B): weathercock principle
Is a supplementary theory specially for wide-beam crafts. A theory as too is able to explain a static turn without sailing speed, plunging Guaras down to windward.
- but perhaps those two points of view can be combined and joined in one only theory
D): Gust and waves
On the sea are phenomenons, as complicate the theories - and disturb a stable course
E): Trim for sail
Every sail-crafts need to be trimmed before sailing out
- but on Guara-rafts it is a bit easier.
Balanced SIDE SLIDING - CE and CLR:
Every sail-craft is playing with the two classic elements - wind and water.
When Thor Heyerdahl in his famous sailing lifted up a Guara for repair, he experienced that the raft changed direction. Without intentions, he changed the underwater hull.
This discovery caused a subsequent research. Thor Heyerdahl's explication is drawn up after consulting and experiments in the Balsa Raft Society in Guayaquil in Equador.
Cite: "In 1953, Emilio Estrada of Guayaquil arranged for a small test raft to be constructed like the Kon-tiki, of nine balsa logs lashed
together and covered by a bamboo deck. Likewise, for navigation, a square sail was hoisted on its usual bi-pod mast in native fashion, and similarly six Guaras were inserted
between the logs, two in the extreme bow and two in the stern. No paddles, rudder or steering-oar were carried on the raft, which was launched from the open coast of Playas, Ecuador,
with a crew of four."
(Ref. Book: Kon-tiki, p.109).
With 12 sketches as cartoon-strip is demonstrated how a raft, equipped with square sail and Guaras mounted along the main trunk, will react on its Guaras under a turn all the clock around.
Explication for the strip of sketches
If we want to change course, we have to lift out a Guara in that end, we want to go leeward.
Without hold in water this end will float away with the wind, while the rest of the Guaras will keep their hold in the water.
Technically the center of Guaras is called CLR = Center of Lateral Resistance.
And it is by lifting or lowering the Guaras in the ends we move, our CLR along and in that way balance and control the side-sliding of respective aft-end and for-end of our raft.
If we lift the front Guaras, the wind press on the CE = Center of Effort = sail /mast-center as will slide the bow sideways, and the raft or the dinghy will pivot around the submerged aft Guaras as a hinge - turn until the Guara-centre and wind-center is on-line in downwind direction. Then the craft is ready to hoist sail and sail off.
Otherwise, if we lift up the aft
Guaras /daggerboard /centerboard, the stern
will side-slide and the craft will now turn up her bow against the wind.
By use of our for and our aft Guaras, we can dominate the pointing of our vessel.
Balanced side-sliding with a dinghy:
The experiment in Guayaquil was followed up in Denmark, where a common sail dinghy was equipped with two in-line Guaras /centerboards.
"The new principle - the use of two 'swinging swords' - makes it possible to alter the pressure of the water from fore to aft under sailing. In other words to steer in this way, and when the vessel is put on course, maintain the course by equalizing the pressure of the water on the fore and aft of the vessel. The new construction works traditionally, so far that vessel and keel skeg works as they have always done."
Research and test by Y.D.Stenild in Denmark. Cite from the Book: "Sejlads på en anden måde - 1986"
bow-centerboard - a fixed keel - aft-centerboard
With both centerboards lowered give us a CLR in the middle - and the boat will sail with wind abeam.
The bow centerboard down and the aft half make the CLR move in front of the mast - and the boat will turn more against wind
Only with the bow centerboard down, we have our CLR above the same centerboard - and the boat will turn bow directly against wind
In both the raft and the dinghy case we are manipulating = changing the shape of the underwater body and in this way moving CLR. CLR is an acronym for the technical 'Center of Lateral Resistance' as expressed popularly is the pivot-center of a craft - and CE is a short term for 'Center of Effort' also called the Wind Center, because it too includes wind forces on hull, cabin and rigging.
The technical /scientific explication on this phenomenon is, that by lowering or lifting the Guaras /centerboards individually we can increase or reduce the front or aft part of the keel and in this way move the CLR from bow to aft, which will play together with CE - Center of Effort, as always will blow to lee of CLR.
Too seen in a cross view with wind across the boat the CE of sail /mast will always go to leeward of the CLR of the hull.
- and behold, a boat will tilt, but a raft almost not.
Sail Dinghy with wind abeam
Viking Replica Kraka with wind abeam
Raft with her Guaras
Balanced side-sliding with a Catamaran
Some pacific double canoes employ the same principle as the Guara-rafts - they are using a handheld paddle for steering.
They are NOT twisting the steer oar, as we do on the Viking ships.
The pacific sailors are holding their paddle on leeward side of one of the hulls, lowering or lifting it to BALANCE THE SIDE-SLIDING.
The paddle itself keep to the boat pressed by water - just as every Lee-bord does.
Photo of Dirch DIPPING his steer paddle. >>>
He is sailing his catamaran on the Carnon River in Cornwall.
The three experiments respectively with raft, dinghy and catamaran show the same empirical result.
YDS extend the natural keel for the dinghy with a centerboard for - and one more aft; and Emilio Estrada places his six Guaras as pairs along the central log. By this arrangement they both can manipulate their Center of Lateral Resistance = CLR in the same way: When lifting up a Guara /centerboard for or aft, that end of our craft loose hold in water and slide sidewards with the wind.
Technically we have changed the shape of the keel and moved the CLR to a new position away from the lifted. Result: the craft now point to a new direction, where CE are going in-line in the wind with the new CLR.
The handheld paddle is handled a little different, but employ the same principle - balance the side-sliding (without need to twist the paddle).
Balanced side-sliding - Conclusion
Balance of side-sliding by Guaras plunged-in as indicated in Guyaquil is enough to steer our vessel, and this is all we need to know for sailing a RAFT.
Note: Your Guara steering is self-adjusting in relation to wind!
In the same way we too can balance a DINGHY - lifting or lowering some Guaras (in the centerboard-version) for and aft - again balancing the side-sliding.
And Dirch in his DOUBLE SAIL-CANOE confirms the same phenomenon.
Everybody can run a boat for the wind - and to sail with wind abeam is neither difficult
"The art of sailing is to beat close hauled to the wind"
That is what will classify to excellence the skill of skippers and his sailing craft
The WEATHERCOCK principle
A sail-raft without any Guara plunged-in is out of control - she has no rudder and will drift with the wind until we plunge down a Guara.
When we then plunge-in a single Guara in any place, we will experience that this Guara will get hold in the water, and the raft will turn just like a wind-vane with this Guara /daggerboard as pivot - turn by the wind press on at least mast and hut of the raft.
That was the discovery of Thor Heyerdahl.
First trial: In stead of lowering two aft Guaras close to the central trunk, we will plunge them in each aft corner - result: the raft will act as before and turn stern against wind. This means that it is not the place along the main trunk as is important.
Second trial: If we then plunge in the same two Guaras in the outermost starboard cleft - alongside the mast, the raft again will turn like a wind-vane on its new pivot. Turn completed, we will find our raft pointing on its new course with wind abeam starboard. Again a static turn without need for streaming water - without sailing.
Behavior as a wind-vane - a Weathercock.
But if such a single set of lonely Guaras is sufficient to keep a sailing course of the whole raft is 'a good question'. It is still not verified nor rejected by any known empiric test.
Behold - more boards
If we want to go even higher to the wind we of course can mount more boards on a steer-neutral place in the mid of the ship, in the same way as we mount leeboards on the many other
- and doing this we expect to reduce the side-sliding with further 6 degrees, as they say they can with lee-boards.
A side leap:
Some catamarans are born with 4 centerboards(fx. Wharram Pahi63)
- and that give the option to steer with Guaras only - as explained by the "weathercock".
They could do it, but skill of that type, we have never heard any skipper cultivate.
The catamarans are sailing on using their two classic rudders.
Opposite monohulls; on a raft we don't need to hang any board on outside. Our raft is wide and build of more trunks, and we can make use of this and plunge in Guaras in the cleft between any trunks - where we like - and not only along the main trunk.
Well, the reason why we in all cases will propose the outermost cleft is the same on all ships: The central area will be difficult to access because of hut and cargo - whereas the outer rim should be more accessible.
So if we apply a board plunged down in the outermost extreme trunk-cleft in lee-side in the neutral zone near mast, it should be OK and work as a Lee-board.
But if we consider the wind-vane principle and combine the wind-vane with our side-board, we of course still can expect our raft beat better - but too obtain a certain directional stability. That means that we should change out the Lee-board with a Luff-board - in the windward side. That is possible, because our board plunged in between trunks will not flap out nor break its suspension, as it would do on a Dutch Lemsteraaken, a Humber Keel or a Thames Barge (a reason why those types of crafts don't use Luff-bord). A raft neither will heel and lift a Luff-board out of water.
Therefor we recommend to mount more Guaras between the two outermost trunks in wind-side and in this way activate the weathervane principle as will help to stabilize your course.
That Luff-board trick is expected to give more stable course and together with less leeway.
We know two things with certainty:
1): Larger distance from CLR (turn point) to CE (wind centre of sail+rig) bring less yaw = shear off - what means less swing out of the weathercock.
2): More Guaras plunged in give more keel and therefor less leeway together with more stability in sail direction - but otherwise: more Guaras reduce the sensibility of each steer-Guara.
Final Advise for the Raft sailors:
Do as the two investigations indicate: Plunge in a pair of Guaras in front end, and a pair more in aft end - and use those two most extreme pairs for steering.
If your raft is well trimmed - that will do it.
If you want more keel to beat higher to the wind, then you could add a leeboard, a centerboard or a luffboard by plunging in some steer-neutral Guaras aside mast and hut. That means in the outer rim, where you have access. First a luff-board in wind side more than in lee-side because of a useful stabilizing wind-vane-effect, but if you want still more keel - then too in center and lee-side - but still steer neutral.
a proposal for distribution of Guara-holders
For and aft for steering - midship to reduce leeway
Even if a Guara is to consider as a fin or a keel; don't fill up your raft-bottom with Guaras! Too many Guaras plunged down too near stem and stern will reduce the impact from your steer-Guaras (or you have to move them all up and down as a set) - having too little influence on the common Center of Lateral Resistance.
In all cases that will be the Guaras most distant from your CE = Center of Effort as will influence most on the CLR = Center of Lateral resistance, and probably those as you will use for steering.
Note that the underwater size of European lee-boards as thumb rule is calculated as 5% of sail area - saying nothing more around dimensions, nothing around 'short and broad' versus 'long and slim', that is your choice, but we have heard of many broken long raft-Guaras.
What we don't know:
Did the Incas use special holders with guiding rail for their Guaras /daggerboards ? or could they plunge them in between the balsa trunks without guiding arrangement - just where they needed them.
If anybody knows what they are doing in Ecuador where they still today employ balsa rafts, we are interested in documentation.
But if you want to use special holders for Guaras on your raft, then it is something to plan and build before sailing out.
In all this we miss some OBSERVATION NOTES from investigators and active ocean sailors, as can back-up or refuse the theories.
Geometrically it is so, that if a skipper need a mean course directly against the wind, he has to tack in zigzag.
If he is able to beat 80 degrees to wind, his sailed distance will be six times the direct distance. If 70 degrees - then 3 times as is far better. If he can make 60 degrees - then only double distance. But if he or his craft will hold over 90 degrees - he can't advance - and he should wait for better wind - or he could take the trade winds around the World. Therefor a surplus of Guaras could be important for 'Luff-board' use.
Balsa rafts and hard weather
Neither a raft nor a Catamaran will heel nor lay down because of wind, and that make the sail geometry much easier, because those crafts move flat on the surface (even if the surface will wave), and a well-adjusted sail with sharp front to cleave the wind should therefor do the job very well. For example a square sail with bowline tightened, fastened to stay or to a raised bowsprit.
A raft is impossible to capsize. In technical terms it has a very high META-CENTRE, and is therefor very stable against rolling and heeling. To roll or turn a somersault theoretically only is possible with a wave as break over, but is never seen for rafts. Therefor a raft can set much more sail than a mono-hull craft. The protest we meet will come from the not-streamlined bunch of trunks pressed too hard and speedy through the water.
But take care, a notable high number of rafts have failed to reach their objective and have given up. Most famous are Thor Heyerdahls Ra-I and Ketin Muñoz' many attempts, but too there is a row of others, whom of one or other reason have needed to give up their purpose. The reasons are many, and often in combination: hard wind, waves and water have sunken many sail-crafts in all historical time.
Rotten, waterlogged or brittle materials, attacks of insects as wood eating ship worms, crafts caught in circular currents or on shore going winds without ability to beat out nor row against wind - and this very often jointed with missing seamanship and too much adventure spirit.
In difficult weather conditions we sometimes need to reduce sail. A reefed square-sail we can't let hang in the yard, fluttering in the wind, only fastened in a long end of the halyard, half down the mast.
On a raft with A-mast (as is without shrouds), we must tie the yard to the lee mast-leg by a sliding parrel or whatever we have. That make crossbars between the mast-legs impossible - at least difficult.
If a log-raft should run for a strong gale, it probably doesn't need any drag-anchor. A such drogue is 'build-in' by the Guaras. The skipper can, by setting his for or aft Guaras, decide to keep his bow or stern against the wind. The raft will behave as a wind-vane.
Stable as a weathercock in the wind.
The Guara-raft will only change direction if the wind does it.
It is a wind-steering system.
Gust and waves complicate the theories
Even in hard weather a raft doesn't need any helmsman with firm hand on a tiller - they say - but that is not quite correct.
A raft will behave stable, if the wind is stable and as long as the waves are small. But wind has gusts and on the ocean rule big waves and swells, and both have as consequence that the forces on the raft are oscillating.
The wind gust is a sudden brief increase in speed of wind - as give certain sheer off, as we on normal crafts counteract by the helm.
When a gust hit the sail, this will try to accelerate the raft, and higher in Beaufort = harder influence. Acceleration means that we shall try to move faster the gross weight of all the raft + cargo.
But very rare it will give an immediate acceleration of speed, because the 'center of gravity' - the point where all the weight of the raft is concentrated, is normally far away from the line, we technically call 'CLR - CE'. When the center of gravity is away from this line, the wind gust not only will accelerate the speed of raft, but will too apply a torque as will try to twist the raft - what in other terms means a 'sheer off' from a steered course.
All heavy weights need time to change speed - Inertia - and the distribution of this weight on the raft surface hold another inertia as delay change in rotation (sheer off).
For rafts as normally have the center of gravity behind the mast, because the cargo is stored more protected there - a rising gust will turn our course leeward: 'lee-helm' - until the gust few seconds after has passed - and then the opposite forces will let the craft fall back again on the course. With only Guaras we have no rudder to counteract that sort of zigzag course, but of course we can lift or lower a Guara to do the same. Please note here: Guara steering is a balanced steering, as doesn't need streaming water - and the raft should therefor after a gust go back to our balanced course - a phenomenon as we still want verified by skippers.
Guys as kite surfers know very well and fear the gusts as is able to lift them out of water - and if that happens, their worry will be their landing.
Raft sliding down a wave - with wind from behind
we don't know who is sailing, but the photo is very illustrative
On Oceans we meet big waves.
When a big wave is passing, the raft will behave like a toboggan and try to "slide down the hill" - if no Guara braking, then with her heavy end in front.
The Weight is concentrated in the gravitation-center, and the gravitation force attacks in this, and together with the wind press on sail and the Guaras seizing the water, trying to hold back any movement, the result will cause another deviation - another shear off in our pointed course - while the wave is passing.
One thing is surfing on the wave slope, but the lift up and later drop down of the water-surface, too has an effect, because it is a vertical acceleration - a heave movement.
It is very difficult to feel the difference between those two movements - heave and toboggan - but not important because they work together as two sides of the same coin. In both the surf and heaving cases the center of gravitation is the point of attack and the weight and its inertia is what resist. The raft will rey to turn its heavy end downwards.
In the common case where we are sailing with wind abeam, and have placed the cargo abaft the mast, the heavy aft-end = the stern of the raft will go down and therefor the bow will turn up against wave crest. And so it is whatever the wave is coming or passing. A sheer-of and back again ! But neither 'weatherhelm' nor 'lee-helm', because it isn't a result of wind.
Passing of waves are too movements as we in normal boats will correct by our tiller.
If we are sailing with wind straight abeam or are drifting with bow against wind and waves there will be no sheer off - as at the picture.
Big waves and gust across our course will cause 'sheer off', and to counteract this, we of course can move some Guaras up or down in the same way, as we use a steering wheel or tiller to keep the control on our course - but we don't need
The Guara-steering is self-adjusting.
Special around TRIM of Rafts
Trim of a balsa raft by Guaras only
- - - in ALL cases a skipper has to check and trim his craft BEFORE setting out on a long voyage - - -
Trim of any sail-craft is done with wind abeam - and sailing along in what is supposed to be a "normal" speed.
On a raft, you can employ, mount and use whatever type of sail and rigging you want, and the trim of your raft will be simple - because you don't need to change anything of hull nor rigging.
The Guaras can change the shape of the underwater body - and we can make this changes sailing along on the ocean.
Because og the flat bottom of the raft, the weight of cargo will not influence much on this trim.
By combining Guaras we can move the pivot-center = the CLR around, where we want to compensate the wind forces on hull, hut and rigging.
By plunging in Guaras, we can move the pivot point of the hull all the 'compass round' the mast - and the wind will then turn the raft just as a weathercock.
The rule is as ever:
the CE = Centre of Effort will blow to lee of CLR = Centre for Lateral Resistance
- just like the mentioned weathercock do -
The steered course is the course pointed by the stem, which for sail vessel (because of leeway) very rare is the same as the real course = course over ground.
The last is the actual progress of vessel as today easiest is defined by GPS.
Many Guaras /daggerboards
This more complicated reality, the skipper has to find out and learn to handle on his actual craft. And good luck to him.
The above theory is explained by a simple model: one mast and few Guaras.
If all cases were so simple with one central mast and a Guara in each corner or end, then our life too could be simple.
- - - but - - -
A):One mast with sail, even if we know that rafts sometimes had more masts and a hut as too would catch wind. That make the determination of a CE = Centre for wind forces more complicated.
B): Ocean going balsa rafts in fact had many Guaras and not only four - typically 6 or even more. At least we should keep some Guaras as counterbalance to wind on hut.
<<< If sail and mast NOT is centered on the raft, we don't need to adjust the mast as we do with stern-rudder crafts.
We only have to put more Guaras under the short end to obtain balance.
And if we raise a hut or a tent we again can counterbalance with more Guaras >>>
As named: More Guaras mean more "keel" to keep a stable course. More Guaras too means that we can make each Guara smaller and therefor more handy or stronger, to avoid the many broken Guaras we hear about. But even so the principle is still, that you shall be able to combine Guaras in such a way, that you can move the CLR = the Common Lateral Centre all the way around the CE - Centre of Effort for all wind forces on the raft (what more or less should be a centre short after a lonely mast itself).
What really give a raft its beating abilities is to apply a concentration of Guaras as luff-boards in the wind-side.
But take care: even if more keel will reduce leeway - as every fin keel do - we repeat the warning: don't fill up your raft bottom with Guaras as will bring you in danger to reduce the effect of the for and the aft Guaras dedicated to steering.